Unfortunately, you will have to try several for yourself. There are no universal blocking reagents that work for all tissues/antibodies. Nonetheless, here is a link to some suggestions: https://www.thermofisher.com/us/en/home/life-science/protein-biology/protein-biology-learning-center/protein-biology-resource-library/pierce-protein-methods/blocking-strategies-ihc.html

From the above site:

>Besides serum, blocking buffers often contain proteins such as bovine serum albumin (BSA), gelatin or nonfat dry milk added at 1-5% (w/v) final concentrations. These inexpensive and readily available proteins either alone or together are present in large excess compared to the antibody concentration, so they compete with the latter for binding to nonspecific sites in the sample. Many labs have a favorite homemade blocking buffer recipe.  However, it is important to make sure that such blocking buffers are free of precipitates and other contaminants that can interfere with IHC detection.

I have used BSA for blocking and it works well. But there are many types of BSA based on purification methods. Some BSA has contaminating peroxidase activity so avoid that if you are using peroxidase-based detection.

Non-fat dry milk is really inexpensive, but you need to try several brands to see if there is anything that interferes with your specific procedure. If you use non-fat dry milk, then you should consider filtering it through a sterile filter (0.22 µm or 0.45 µm) into a sterile bottle and store it as frozen aliquots, otherwise you will get fungal/bacterial growth in it.

I agree with David above.  I'm not sure there is a need to use commercial products when milk, BSA, or serum tends to work well.  Additionally, you can make it fresh and forgo sterilizing it.  I will add that milk may inhibit detection of phospho-epitopes.  Good luck.

Hallo Magdalena, it depnds on your detections system that you are using. If you are working with labelled secondary antibodies it is enough to block with 10 % normal serum from those animal in which  your secondary ab is generated  (Goat-Anti-rabbit Alexa488 ---> normal Goat).  I have also made good expiernces with 1% BSA in TBS-Tween or 0.2% TBS-Triton. If you are working with ABC or Strepavidin  I recomand to buy the AB-blocking kit from those company from which you have bought your detection system. Good luck!